Conduct-disordered behavior in preschool-age children constitutes the single most important behavioral risk factor for later antisocial behavior. Research suggests that certain family characteristics put children at risk for developing conduct problems and that several of these factors are present at high levels in Head Start families. Early identification and intervention is a cornerstone of the Head Start program and the program's performance standards require that effective services be provided to children deemed at-risk for developing conduct problems. Parent Child Interaction Therapy (PCIT) is a brief, empirically-supported treatment for conduct-disordered preschool children. However, PCIT has never been systematically studied for its effectiveness with Head Start families. The goal of the present study is to screen for behavior problems in preschool children enrolled in Head Start and to examine the effectiveness of PCIT in a sample of Head Start families whose children are at risk for the development of later conduct problems. In addition, normative data on Head Start families will be gathered for the measures used in the treatment outcome study to provide a relevant source of reference in the examination of PCIT outcome in this population. Families of children with behavior problems in the clinical range will be randomly assigned to standard care, as provided by the Head Start program, or to standard care plus PCIT. Assessments will be performed at pretreatment and posttreatment, and maintenance data will be collected at 6 months following treatment completion. The knowledge gained from this study will inform the development of strategies relevant in conducting behavioral family treatments with Head Start families.